Hydro-conversion of 1-methyl naphthalene into (alkyl)benzenes over alumina-coated USY zeolite-supported NiMoS catalysts

Hydro-conversion reactions were carried out at 360 °C under 5 MPa of H2 pressure to study ring opening reactions of 1-methyl naphthalene using NiMoS supported on γ-alumina and alumina-coated/mixed USY zeolites. The catalysts were characterized using N2 BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), pyridine FT-IR, and high-resolution transmission electron microscopy (HR-TEM) to study the influence of morphological and acidic properties on hydrogenation (HYD) and hydrocracking (HC) reactions. NMACZ-2 (NiMoS supported on the minimum amount of alumina-coated USY zeolite) showed enhanced reactivity for HC and produced (alkyl)benzenes with the highest yield, of ca. 80%. By-products were tetralin, decalin and cyclo-paraffin species. The tetralin species produced using NMACZ-2 moved into the alumina-coated USY zeolite support before undergoing HYD to produce decalin species, which were rapidly and selectively hydro-cracked into (alkyl)benzenes. A large amount of decalin was produced through the HYD of tetralin without significant cracking, possibly due to the weak acid character of γ-alumina. Bulk phase Mo oxide species on NMAZ (physical mixture of alumina and USY zeolite), as well as deactivation of the catalysts due to coke formation over the naked zeolite surface, inhibited the ring opening of tetralin, decreasing the yield of (alkyl)benzene. Various morphologies, such as the MoS2 structure and acidic characteristics of the catalysts, were crucial factors affecting the HC reactivity of 1-methyl naphthalene.